In automatic web rewinding machines of the type to which this invention relates, a number of core supporting mandrels--typically six--are mounted on an indexingly rotatable turret. The mandrels extend parallel to the horizontal axis about which the turret rotates, and they are spaced at equal distances from the turret axis and at uniform intervals around that axis. A six-mandrel turret moves through one-sixth of a revolution at each of its indexing movements, and hence it carries each mandrel in turn to each of six successive stations, with a period of dwell at each station.
In this case, one station--which could be considered the first one--is a loading station at which a length of core stock is slid axially onto the mandrel. At the next station the core stock is slitted into shorter lengths, each corresponding to the width of an individual roll, and glue is applied to the core. At the third station the mandrel is brought up to winding speed, and as the mandrel is moving from the third to the fourth station the web is attached to the glued core on the mandrel, for the beginning of the winding operation. Winding continues while the mandrel is at the fourth station, and as it moves out of that station the web is cut through across its width to sever it from the wound roll and give it a new leading edge that is attached to a new core on a mandrel moving into the winding station. At the fifth station the rotation of the mandrel is decelerated to a stop, and at the sixth station the wound core or "log" is stripped off of the mandrel. The mandrel then moves to the first station for a repetition of the cycle.
The turret by which the mandrels are carried comprises a spider which is mounted for rotation on a coaxial shaft that projects a substantial distance in one direction from the spider. The mandrels have rotating connections with the spider, and they project from it in the same direction as the turret shaft. The rotating connection of each mandrel with the spider must provide for cantilevered support of the mandrel because, when the mandrel is at the core loading station and the unloading station, its end remote from the spider has to be accessible to allow cores to be moved axially onto and off of it. But the mandrels tend to be rather heavy and very long--72 in. to 96 in. is typical--and therefore their free ends should be supported whenever possible, and certainly during winding.
To provide for support of the free ends of the mandrels, there is conventionally an assembly of supporting arms or chucks on the end portion of the turret shaft that is remote from the spider. This assembly, which is constrained to indexing rotation with the spider, comprises a chuck arm for each mandrel. Each chuck arm is swingable about an axis which is near the turret axis and transverse thereto, between a substantially radially extending closed position in which the free end of the chuck arm supportingly engages the free end portion of its mandrel and an open position in which the chuck arm is disengaged from its mandrel and is disposed in a more or less axial orientation alongside the turret shaft. Each chuck arm is operated automatically so that it is in its open position during loading and unloading of the mandrel and is in its closed position at least from the time the mandrel moves into the gluing and core slitting station until it moves out of the deceleration station.
The heretofore conventional mechanism for actuating the mandrel supporting chuck arms in an automatic web rewinder is illustrated in U.S. Pat. No. 2,769,600, to Kwitek et al. It comprised a barrel cam that was fixed to the machine frame adjacent to the free ends of the mandrels, and a lever and link arrangement for each chuck arm, each such arrangement being carried by the turret for rotation therewith and having a cam follower roller that rode in a groove in the periphery of the stationary barrel cam. Each chuck arm was thus actuated at appropriate times in consequence of indexing movement of the turret. The shape of the cam groove was said to be such that the chuck arms moved into engagement with their respective mandrels when the latter were "generally adjacent the glue applicator wheels" and retracted when the mandrels moved "from the web winding position."
Stripping of wound rolls off of a mandrel is conventionally accomplished by means of a pusher that engages the log at only one side of the mandrel and thus tends to impose a lateral force upon the cantilevered mandrel that can set it into a vibration which may be aggravated by the indexing movement that follows unloading. With the mandrel unsupported at the loading station, its free end often wobbled so severely that a core could not be run onto it with automatic core loading equipment.
With heretofore conventional machines, failure to load a core created a danger that the mandrel itself would be coated with glue at the gluing station, necessitating a lengthy shutdown of the machine for cleaning. When the operator saw that an unloaded core was moving out of the loading station, he could and did stop the machine, but because of the nature of the chuck arm actuating mechanism, there was no way to retract the chuck arm engaged with the empty mandrel, to permit manual loading of a core onto it axially. The conventional solution to this problem was to slit a core along its length and push it laterally onto the mandrel, to protect the mandrel from glue; and then, at the conclusion of the winding cycle, discard the individual rolls wound onto that slitted core.
The Kwitek et al patent recognizes that wobble of an unsupported mandrel end could cause a chuck arm to fail to engage the mandrel properly. It discloses a U-shaped member on each chuck arm, intended to preliminarily engage the mandrel during closing movement of the chuck arm and steady the mandrel sufficiently to enable its conical free end to be received in the bearing socket in the chuck arm. Unfortunately, this expedient was not always successful in practice, and when the wobbling mandrel failed to enter the chuck arm socket, the cam operated chuck arm mechanism exerted as much force as the indexing mechanism could impose, with inevitable bending or breakage of the link and lever elements that translated cam follower motion into swinging motion of the chuck arm. Repair of such damage was difficult and time consuming.
One expedient that has been used to prevent damage to the chuck arm actuating mechanism was to mount the barrel cam for limited axial motion and pneumatically bias it towards one limit of such motion. When a chuck arm failed to close properly, the reaction force that was imposed upon the cam moved it against its bias to a position at which it actuated an emergency stop switch that shut down the machine until the operator could investigate and correct the malfunction. However, this emergency shut-down arrangement, like the U-shaped mandrel damping member disclosed by Kwitek et al, merely relieved some of the effects of the problem rather than solving the problem itself. For example, it still did not permit axial loading of a core onto an empty mandrel that had moved out of the loading station.
One side effect of the prior mechanism for actuating the chuck arm is worth noting, although it probably received little recognition. The primary drive for chuck arm actuation was essentially the indexing mechanism for the turret, through which all forces needed for such actuation had to be delivered. The chuck arm mechanism thus contributed to the load on the indexing mechanism (especially upon failure of a chuck arm to close properly) and in turn increased the wear on the indexing mechanism with corresponding decrease in indexing accuracy.